TRACE GAS FLUX MEASUREMENT (N2O, CO2, CH4) FROM AN ALFALFA FIELD

Excess application of animal waste to crops can result in an enhanced emission of greenhouse gases to the atmosphere resulting in global warming and destruction of the ozone layer. To quantify emissions in the Mediterranean environment as a function of soil water regime, an experimental trial was conducted on a field crop in Southern Italy. Three 35 m diameter circular plots were established on a 2 years old alfalfa crop. Two plots were initially fertilized with chicken manure but only one was irrigated, the third one was used as control. The field was mown last on June 7, 1999. The watered plot received a further fertilization and irrigation following grass mowing. N2O, CO2 and CH4 air concentrations were measured from vented closed chambers using a Photo Acoustic Infrared Detector. The fluxes were calculated through non-linear regression of the headspace concentration increase. Measurements started the day after the plot was fertilized-irrigated for the second time. N2O emission peaked the first day after fertilization and irrigation, dropped on the second day and was about zero after 7 days. Total N2O emission from the irrigated plot over the measurement period was 32.3 ± 5.3 mg N2O-N m-2. CO2 fluxes from the irrigated plot were highest in the morning after fertilization and total emission from the irrigated plot was 35.5 ±7.1 g CO2-C m-2. The CH4 emission peaked the morning (9h30 - 12h30) after fertilization and decreased in the afternoon (14h30 - 17h00). The flux dropped further during the morning of the next day but showed a slight increase in the afternoon. Total emission at the irrigated plot was 61.9 ± 7.7 mg CH4-C m-2